The present invention resides generally in the field of cardiology, and more particularly relates to stable myocardial grafts and methods and cellular compositions useful for achieving such grafts.
As further background, organ transplantation has been widely used to replace diseased, nonfunctional tissue. More recently, cellular transplantation to augment deficiencies in host tissue function has emerged as a potential therapeutic paradigm. One example of this approach is the well publicized use of fetal tissue in individuals with Parkinsonism (reviewed in (1), see reference list, infra.), where dopamine secretion from transplanted cells alleviates the deficiency in patients. In other studies, transplanted myoblasts from uneffected siblings fused with endogenous myotubes in Duchenne""s patients; importantly the grafted myotubes expressed wild-type dystrophin (2).
Despite their relevance in other areas, these earlier studies do not describe any cellular transplantation technology which can be succesfully applied to the heart, where the ability to replace damaged myocardium would have obvious clinical relevance. Additionally, the use of intra-cardiac grafts to target the long-term expression of angiogenic factors and ionotropic peptides would be of therapeutic value for individuals with myocardial ischemia or congestive heart failure, respectively.
In light of this background there is a need for the development of cellular transplantation technology in the heart. Desirably, such technology would not only provide stable grafts in the heart but also enable the delivery of useful recombinant proteins or other molecules directly to the heart. The present invention addresses these needs.
The applicant has established cellular grafts in the myocardium which are viable long-term. Cardiomyocytes and skeletal myoblasts have been grafted directly into the myocardium of syngeneic animals. Viable grafts were detected at least one-half year post-implantation (the latest time point assayed). The presence of the grafts was not accompanied by overt cardiac arrhythmia, and the majority of the grafts were juxtaposed directly to the host myocardium and not encapsulated. It has thus been discovered that the myocardium can serve as a stable platform for cellular transplants. These transplants can be used for the local delivery of recombinant molecules to the heart and/or for replacing diseased tissue to supplement myocardial function.
Accordingly, one preferred embodiment of the invention provides a myocardial graft in an animal which includes a stable graft of skeletal myoblasts or cardiomyocytes incorporated in myocardial tissue of the animal.
Another preferred embodiment of the invention provides a method for forming a stable myocardial graft in an animal. The inventive method includes the step of introducing skeletal myoblasts or cardiomyocytes in myocardial tissue of the animal so as to form a stable myocardial graft. The cells can be conveniently introduced, for example, by injection.
Another preferred embodiment of the invention provides a method for delivering a recombinant molecule to myocardial tissue of an animal. This method includes the step of establishing a stable graft of skeletal myoblasts or cardiomyocytes incorporated in myocardial tissue of the animal, wherein the myoblasts or cardiomyocytes deliver the recombinant molecule to the myocardial tissue. In this embodiment the myoblasts or cardiomyocytes will carry transgenes encoding the recombinant molecule.
Another preferred embodiment of the invention provides a cellular composition comprising a substantially homogeneous population of non-immortalized cardiomyocytes. This and other cell populations can be obtained utilizing a preferred inventive method that includes (i) transfecting embryonic stem cells to introduce a marker gene enabling selection of one cell lineage from other cell lineages resulting from differentiation of the stem cells, (iii) causing the stem cells to differentiate, and (iv) selecting said one cell lineage based on the marker gene. The cells used in and resulting from such methods also form a part of the present invention.
Still another preferred embodiment of the invention provides a non-human animal having a stable graft of skeletal myoblasts or cardiomyocytes incorporated in myocardial tissue of the animal.
The invention thus provides myocardial grafts, methods and cellular compositions useful for forming myocardial grafts, and animals which have the myocardial grafts. The grafts will find use both as a vehicle for delivering therapeutic substances such as recombinant proteins and other molecules, and as a means for replacing diseased tissue to supplement myocardial function. Cellular compositions of the invention can be used directly to prepare grafts, and will also be useful in screening drug substance effects on cardiomyocytes and for expressing and obtaining recombinant proteins. Grafted animals can be used, for example, to screen the effects of recombinant molecules on the heart.
These and other objects and advantages of the invention will be apparent from the following description.